Conductive materials include conductive paste, conductive adhesives, anisotropic conductive films, etc., and for this conductive material, a conductive composition comprising conductive fine particles and a resin is used. With respect to the conductive fine particles, there are generally used metal powder, carbon powder, fine particles having a metal plating layer on the surface, etc.
Manufacturing methods for such conductive fine particles having a metal plating layer on the surface are disclosed by for example, the following Japanese Kokai Applications: Sho-52-147797, Sho-61-277104, Sho-61-277105, Sho-62-185749, Sho-63-190204, Hei-1-225776, Hei-1-247501 and Hei-4-147513.
Among these manufacturing methods, when carrying out plating on fine particles having a particle size of not less than 5000 μm, barrel plating devices are generally used. In the barrel plating device, a plating target is put inside a rotatable barrel having a polygon cylinder shape in which a plating solution is contained, and while the barrel is being rotated, electroplating is carried out by allowing the plating target to contact the cathode placed inside the barrel.
However, when plating is carried out on fine particles having a particle size not more than 5000 μm by a method using the barrel plating device, problems arise in it that fine particles in an aggregated state are subjected to plating in the plating solution, failing to form mono-particles and in it that particles are not plated uniformly, causing an irregular plating layer.
In order to solve these problems, for example, the following plating devices have been proposed: Japanese Kokai Publication Hei-7-118896 discloses a manufacturing device for conductive fine particles which comprises a disk-shaped bottom plate secured to the upper end of a perpendicular driving shaft, a contact ring for conducting electricity placed on the upper face of the porous member, a porous member that is placed in the vicinity of the contact ring and that allows only a plating solution to pass there through, a hollow cover of a trapezoidal cone shape having an opening on its upper center portion, a treatment chamber formed in a manner so as to sandwich the contact ring between the outer circumferential portion of the hollow cover and the bottom plate, a supply tube for supplying the plating solution to the treatment chamber through the opening, a container for receiving plating solution scattered from the pores of the porous member, a drain tube for draining the plating solution accumulated in the container, and an electrode inserted through the opening to contact the plating solution, wherein, during the plating process, rotation and stoppage or speed reduction are repeated.
Japanese Kokai Publication Hei-8-239799 discloses a manufacturing device for conductive fine particles, in which the contact ring and the porous member are integrally connected.
Japanese Kokai Publication Hei-9-137289 discloses a manufacturing method for conductive fine particles, wherein a plating device, comprising a rotatable plating device main body having a filter section formed on at least one portion of its outer circumferential section and a cathode as a contact ring formed on the outer circumferential section and an anode placed inside the main body so as not to contact the cathode, is used for forming a plating layer on the surface of the fine particles put inside the main body, while the main body is rotated centered on its rotation axis and the plating solution is supplied to inside of the main body.
In these manufacturing devices for conductive fine particles, a plating target is pressed onto the contact ring by a centrifugal force, and rotated, and stopped or reduced in the speed repeatedly, therefore, the conductivity is improved even in the uniformly mixed state, the current density is increased, and the update of the plating solution is frequently carried out so that the fine particles are free from aggregation in the plating solution, thereby making it possible to obtain conductive fine particles having a plating layer with a uniform thickness.
However, the following problems arise in these manufacturing devices for conductive fine particles.
The pore size of the porous member and the number of revolutions (peripheral velocity) of the treatment chamber are appropriately selected in accordance with the particle size of fine particles as plating targets. In the case when fine particles having a particle size of not more than 100 μm are subjected to plating, it is necessary to increase the peripheral velocity of the treatment chamber so as to make the particles contact the contact ring. For example, in the case of fine particles having a diameter in the range of 60 to 100 μm, the pore size of the porous member needs to be set to not less than 20 μm and the peripheral velocity needs to be set to not less than 300 m/min. It is confirmed that the peripheral velocity not more than this value is hard to allow the fine particles to contact the cathode (contact ring) and plating deposition is sometimes not carried out.
However, when the peripheral velocity of the treatment chamber is increased, the plating solution is subject to a force in the outer circumferential direction by the function of a centrifugal force so that the plating solution forms a vortex having a mortar-like shape inside the treatment chamber, gradually rises along the inner wall of the hollow cover, and is scattered from the opening of the hollow cover. As a result, the problem arises in it that the fine particles flow out (overflow) from the treatment chamber together with the scattered plating solution. In addition, if the amount of the liquid within the treatment chamber is reduced so as to prevent the overflow, the area in which the electrode in contact with the plating solution is reduced, with the result that the current density is reduced and further the formation of a vortex causes the electrode to be exposed, resulting in no contact with the plating solution and no current flow.
Because of these problems, it have been impossible to actually carry out plating on fine particles of not more than 100 μm.
Moreover, with respect to the pore size of the porous member, those pore sizes not allowing a plating solution to pass there through have been adopted, and several kinds of porous members have been used in accordance with the particle size of the fine particles.
However, since these porous members are filter-shaped porous members made of plastics or ceramics having communicating bubbles, the pore sizes within the porous members have considerably much variation. For this reason, at portions where the pore sizes of the porous members are the same as or greater than the particle size of the fine particles, clogging and particle losses occur at the time of passage of the particles. Moreover, when a porous member of not more than 20 μm is used, the resistance at the time of the passage of the plating solution through the porous member becomes greater, as a result that the amount of passage of the plating solution through the porous member is remarkably reduced. When clogging occurs in this state, the plating solution within the treatment chamber is hardly circulated and/or updated, with the result that problems such as a liquid temperature rise within the treatment chamber and variations in the composition of the plating solution occur, causing serious adverse effects on the quality of the plating layer.
Moreover, in the case of these prior art manufacturing devices for conductive fine particles, it has been confirmed that, when electroplating is carried out on fine particles of approximately not more than 100 μm, aggregation occurs as the electroplating progresses, and there is a limit in efficiently carrying out electroplating on each of the fine particles.
In prior art manufacturing methods for conductive fine particles, an electric current is applied and electroplating is carried out in a state where the fine particles is being pressed against the contact ring (cathode) by the function of a centrifugal force due to rotation of the treatment chamber. Here, at the time of stoppage of the power application, the rotation is also stopped, with the result that the fine particles are dragged by gravity and the flow of the plating solution due to inertia, made to drop on the flat surface of the central portion of the bottom plate, and mixed. When the treatment chamber is rotated next time, they are pressed against the contact ring in a different attitude while being mixed, and subjected to electroplating. By using this repeated cycle of rotation and stoppage, an attempt is made to form a plating layer having a uniform thickness on each of the fine particles contained in the treatment chamber.
However, in this conventional manufacturing method for conductive fine particles, the following problems arise.
In the conventional manufacturing method for conductive fine particles, a given time is provided from the start of rotation of the treatment chamber to the start of the application of power, and during this time, the fine particles are shifted to the contact ring (cathode) (hereinafter, this time is referred to as “particle shifting time”). Next, the power application is started while the treatment chamber is being rotated at a constant speed, an electric current is applied to the fine-particle lumps contacting the contact ring, so that a plating coat film is deposited (hereinafter, this time is referred to as “power application time”). Further, at the time of the stoppage of the power application, the rotation speed of the treatment chamber is reduced gradually in a predetermined time (hereinafter, this time is referred to as “speed reduction time”) so that the treatment chamber is temporarily stopped (hereinafter, this time is referred to as “stoppage time”). The process is repeated with this cycle as one cycle.
In this case, in order to improve the efficiency of plating, it is necessary to set the power application time longer or to increase the current density at the time of power application.
However, since the fine particles are allowed to contact the contact ring (cathode) in a state of aggregated fine-particle lumps, when a plating coat film is deposited in this state by applying power for a long time, some particles are subjected to plating in the aggregated state, as a result to occur a problem of aggregation lumps. In other words, in order to prevent the occurrence of aggregation lumps, the power application time cannot be set much longer.
Moreover, when the current density is increased higher, the amount of deposition of the plating coat film becomes too high within the power application time in one cycle, as a result to occur in a problem of aggregation lumps. This is presumedly because the too much amount of deposition of the plating coat film in one cycle causes a deposition of a thick plating coat film covering the surface of aggregated fine-particle lumps, thus, it is not possible to break the plating coat film covering the surface of fine-particle lumps by using only a stirring force at the time of the stoppage of the treatment chamber, and another plating coat film is again deposited on the surface thereof at the next power application.
Furthermore, the following problems arise in the prior art manufacturing methods for conductive fine particles. In the case when plating is carried out on fine particles having a small specific gravity, since there is little difference between their specific gravity and the specific gravity of the plating solution, there is a delay in their approach to the contact ring, and when power is applied before they have completely approached the contact ring, the conductive base layer tends to melt down due to the bipolar phenomenon. The bipolar phenomenon refers to a phenomenon in which in the case when contact force between the plating target and the cathode is weak, or in the case when power is applied before the plating target has contacted the cathode, the plating target itself is subjected to polarization, and the coat film melts down from portions getting positively charged.
In particular, in the case of fine particles to which electric conductivity is imparted by forming a conductive base layer of angstroms on the surface of the non-conductive fine particles, such as organic resin fine particles and inorganic fine particles, by using the electroless plating method, etc., when the bipolar phenomenon occurs, the conductive base layer melts down and the fine particle surface loses its conductivity, failing to carry out electroplating.
Moreover, in the case when the power application time is too short, since the application of power is started before all the fine particles have approached the contact ring, the bipolar phenomenon occurs, failing to carry out electroplating. In contrast, when the power application is too long, the ratio of the power application time within one cycle becomes smaller, resulting in degradation in the efficiency.
Here, anisotropic conductive adhesives have been widely used so as to electrically connect small-size parts such as semiconductor elements to a substrate, or to electrically connect substrates with each other, in the field of electronics products such as liquid crystal displays, personnel computers and portable communication devices.
With respect to these anisotropic conductive adhesives, binder resins in which conductive fine particles are blended have been widely used. With respect to such conductive fine particles, those particles made by applying metal plating onto the outer surface of organic base particles or inorganic base particles have been widely used. With respect to these conductive fine particles, various techniques have been disclosed, for example, by Japanese Kokoku Publications Hei-6-9677, Japanese Kokai Publication Hei-4-36902, Hei-4-269720 and Hei-3-257710.
Moreover, with respect to anisotropic conductive adhesives in which these conductive fine particles are blended in binder resins so as to form films and paste, various techniques have been disclosed by for example, Japanese Kokai Publications Sho-63-231889, Hei-4-259766, Hei-2-291807, and Hei-5-75250.
In anisotropic conductive adhesives based on these techniques, those adhesives that use conductive fine particles comprising a conductive layer on an electric insulating material by electroless plating have been widely adopted. However, the conductive layer formed by electroless plating generally cannot be made thicker, resulting in a problem of little current capacity at the time of connection.
For this reason, in an attempt to ensure the conductivity and to increase the current capacity at the time of connection, plating by noble metal has been adopted, however, since it is difficult to directly plate the noble metal on an insulating material, a method in which base metal such as nickel is first plated by electroless plating, and noble metal is then substitute-plated has been adopted. In the substitution reaction in this case, the surface of the base metal layer is not completely substituted, and a part of the base metal remains, therefore there is a possibility that this part gradually deteriorates, failing to provide sufficient reliability.
In particular, in recent years, miniaturization has been achieved in electronic apparatuses and electronic parts, with the result that wiring for substrates, etc., becomes finer and reliability in connecting sections has been demanded acutely. Moreover, with respect to elements to be adopted for plasma displays that have been developed recently, since these elements are of the large-current driven type, anisotropic conductive adhesives which are suitable for large electric currents have been demanded. In order to solve the problem with current capacity, there is another method to increase the concentration of the conductive fine particles, however, an increased concentration causes another problem of the possibility of leakage between electrodes.
Meanwhile, electronic circuit elements, such as semiconductor elements, quartz oscillators, and photoelectric transfer elements, are connected to an electronic circuit substrate to form an electric circuit part, thus, these are utilized in various forms in the field of electronics. Various techniques have been developed with respect to connection of these electronic circuit elements to electronic circuit substrates.
Japanese Kokai Publication Hei-9-293753 has disclosed a technique in which a conductive ball is used in order to improve the connecting property of an electronic circuit element and an electronic circuit substrate without applying any specific additional process to the respective electrode sections. However, this technique fails to solve the following various problems systematically.
Japanese Kokai Publication Hei-9-213741 discloses a semiconductor device wherein a semiconductor chip and an organic printed wiring substrate are connected with each other by solder and the entire surface, etc. of the connected section is coated with an insulating organic sealing material. However, this technique requires time-consuming tasks, and also fails to solve various problems with connecting sections systematically.
Upon manufacturing an electronic circuit part by connecting electronic circuit elements to an electronic circuit substrate, various problems arise due to the connecting property of the connecting section, and various techniques have been used so as to solve these problems.
Here, these prior art techniques are collectively described as follows by exemplifying a case in which an IC bear chip as a semiconductor element is connected to an electronic circuit substrate.
(1) Wire Bonding Method
Peripheral electrodes of the IC chip and the electronic circuit substrate are heated and press-bonded by using thin wires of gold or copper so as to connect to each other. This wire bonding method has an advantage in that wire connection is made without applying any processing to aluminum electrodes in the IC chips, however, in contrast, it has disadvantages in that the connecting pitch is not made smaller and in that the connecting section becomes bulky.
(2) Flip Chip Bonding Method by Using Solder Bumps (for Example, Japanese Kokai Publication Hei-9-246319)
Solder bumps are formed on the electrode sections of the IC bear chip, and are superposed on the electrode sections of the electronic circuit substrate, and heated so that connection is formed by molten solder (FIG. 36). The formation of solder bumps is made by a method in which after forming a multi-layer metal barrier layer on the aluminum electrodes of the IC chip, solder plating is carried out and then heated, or in which solder balls are placed on the electrode sections, and then heated.
The flip chip bonding method by solder bumps has an advantage in that positioning between the electrodes is easily carried out because of the self-alignment effect of the solder. In contrast, problems arise in it that a multi-layer metal barrier layer has to be formed on the aluminum electrodes of the IC chip, that the gap cannot be maintained constant due to molten solder bump sections, and that the solder bump sections are subjected to “shearing deformation” exerted by the difference in the thermal expansion coefficient between the IC bear chip and the electronic circuit substrate, with the result that cracks tend to occur in the connected section between the solder bump sections and the substrate electrode sections, resulting in degradation in the connecting reliability.
(3) Flip Chip Bonding Method by Using a Solder Coat Ball Having a Highly Rigid Core (for Example, Japanese Kokai Publications Hei-9-293753, Hei-9-293754, Hei-5-243332), Hei-7-212017)
For example, balls coated coating copper core with solder are placed on the electrode sections on an IC chip, and then heated so that the solder coat balls are secured to the electrode sections on the IC chip; then, the secured solder coat balls are superposed on the electrode sections of an electronic circuit substrate, and then again heated so as to make connection (FIG. 47). In the same manner as (2), in this method also, “shearing deformation” is exerted due to the difference in the thermal expansion coefficient between the IC bear chip and the electronic circuit substrate, with the result that cracks tend to occur in the connected sections between the solder coat balls and the substrate electrode sections, resulting in degradation in the connecting reliability.
(4) Flip Chip Bonding Method by the Bump Transfer Method
A gold bump formed on a bump forming substrate is transferred and placed on a lead portion of a tin- or gold-plated film carrier formed by thermal press bonding at the first stage, and next, after an IC chip has been superposed thereon, the second srage thermal press bonding is carried out (FIG. 48). This method has an advantage in that the formation of metal barrier layer is not required on the aluminum electrodes on the IC chip. In contrast, a particularly high pressure needs to be applied at the second stage thermal press bonding, resulting in a possibility of damage to the IC chip performance.
(5) Flip Chip Bonding Method by Using Bumps Comprising Conductive Resin
A conductive resin comprising silver powder and an epoxy-based adhesive is formed into a bump shape with a thickness of approximately 10 μm by a screen printing method on the electrode sections of an IC bear chip, and this is heated to be cured, and after being superposed on the electrode sections of an electronic circuit substrate, connection is performed by using another conductive adhesive (FIG. 49). This method has advantages in that upon connection, no expensive materials are required while only a simple process is used. In contrast, problems arise in that special electrodes, made of nickel/palladium, etc., have to be added to the aluminum electrodes of the IC chip, and in that the bump section is susceptible to plastic deformation, with the result that the connection reliability may deteriorate.
(6) Flip Chip Bonding Method by an Anisotropic Conductive Adhesive
Metal fine particles of approximately 5 μm, or conductive fine particles applying metal plating to resin core fine particles, are blended with a thermoplastic or thermosetting adhering resin to form a liquid or a film-shaped anisotropic conductive adhesive, and by using this anisotropic conductive adhesive, gold bump sections formed on the aluminum electrodes of an IC chip and the electrode sections of an electronic circuit substrate are joined to each other by thermal press bonding (FIG. 50). This method has an advantage in that upon joining, no reinforcing seal resin, which is required in the above-mentioned (1) to (5), for filling the gap between the IC chip and the electronic circuit substrate is required. In contrast, because of the necessity of installing the gold bump, problems arise in that the conductive fine particles enter the gap section other than the gap between the IC chip and the electrode sections of the electronic circuit substrate, resulting in a reduction in the insulating resistivity between adjacent electrodes and the subsequent possibility of a short circuit between the electrodes.
In order to solve the above-mentioned problems with the prior art techniques (1) to (6), the following devises are proposed:
In the wire bonding method (1) and the flip chip bonding method by using solder bumps (2), in order to solve the problem of the difficulty in high-density packaging with pitches of not more than 100 μm, an attempt is required to join an IC chip with high density wiring to an electronic circuit substrate.
In the flip chip bonding method by solder bumps (2) and the flip chip bonding method by using a solder coat ball having a highly rigid core (3), in order to solve the problems in which shearing deformation is exerted due to the difference in the thermal expansion coefficient between the IC chip and the electronic circuit substrate with the result that cracks tend to occur in the connected sections between the solder bumps or the solder coat balls and the substrate electrode sections, resulting in degradation in the connecting reliability, and in order to solve the problem in which, in the flip chip bonding method by bumps made of conductive resin (5), the bump section is susceptible to plastic deformation with the result that the connection reliability may deteriorate, an attempt is required to improve the connection reliability in the electronic circuit parts comprising IC chips and electronic circuit substrates.
In the filp chip bonding method by the use of the bump transfer method (4), in order to solve the problem in which a particularly high pressure needs to be applied at the second stage thermal press bonding, resulting in a possibility of damage to the IC chip performance, an attempt is required to eliminate the need for applying a high pressure in the attaching process between the IC chip and the electronic circuit substrate.
In the flip chip bonding method by an anisotropic conductive adhesive (6), in order to solve the problem in which the conductive fine particles enter the gap section other than the gap of the electrode sections with the result that the insulating resistivity between the adjacent electrodes is reduced, an attempt is required to prevent the reduction in the insulating resistivity between the adjacent electrodes of the IC chip and electronic circuit substrate.
In order to solve the problems with the prior art, attempts have been required to solve all the above-mentioned problems.